Fix replica identity check for MERGE.

When executing a MERGE, check that the target relation supports all
actions mentioned in the MERGE command. Specifically, check that it
has a REPLICA IDENTITY if it publishes updates or deletes and the
MERGE command contains update or delete actions. Failing to do this
can silently break replication.

Author: Zhijie Hou <houzj.fnst@fujitsu.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Dean Rasheed <dean.a.rasheed@gmail.com>
Tested-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/OS3PR01MB57180C87E43A679A730482DF94B62@OS3PR01MB5718.jpnprd01.prod.outlook.com
Backpatch-through: 15

src/backend/executor/execMain.c

@@ -1061,6 +1061,15 @@ CheckValidResultRel(ResultRelInfo *resultRelInfo, CmdType operation,
 	{
 		case RELKIND_RELATION:
 		case RELKIND_PARTITIONED_TABLE:
+
+			/*
+			 * For MERGE, check that the target relation supports each action.
+			 * For other operations, just check the operation itself.
+			 */
+			if (operation == CMD_MERGE)
+				foreach_node(MergeAction, action, mergeActions)
+					CheckCmdReplicaIdentity(resultRel, action->commandType);
+			else
 				CheckCmdReplicaIdentity(resultRel, operation);
 
 			/*

src/test/regress/expected/publication.out

@@ -1947,6 +1947,34 @@ INSERT INTO testpub_insert_onconfl_parted VALUES (1, 1) ON CONFLICT DO NOTHING;
 DROP PUBLICATION pub1;
 DROP TABLE testpub_insert_onconfl_no_ri;
 DROP TABLE testpub_insert_onconfl_parted;
+-- Test that the MERGE command correctly checks REPLICA IDENTITY when the
+-- target table is published.
+CREATE TABLE testpub_merge_no_ri (a int, b int);
+CREATE TABLE testpub_merge_pk (a int primary key, b int);
+SET client_min_messages = 'ERROR';
+CREATE PUBLICATION pub1 FOR ALL TABLES;
+RESET client_min_messages;
+-- fail - missing REPLICA IDENTITY
+MERGE INTO testpub_merge_no_ri USING testpub_merge_pk s ON s.a >= 1
+ WHEN MATCHED THEN UPDATE SET b = s.b;
+ERROR:  cannot update table "testpub_merge_no_ri" because it does not have a replica identity and publishes updates
+HINT:  To enable updating the table, set REPLICA IDENTITY using ALTER TABLE.
+-- fail - missing REPLICA IDENTITY
+MERGE INTO testpub_merge_no_ri USING testpub_merge_pk s ON s.a >= 1
+ WHEN MATCHED THEN DELETE;
+ERROR:  cannot delete from table "testpub_merge_no_ri" because it does not have a replica identity and publishes deletes
+HINT:  To enable deleting from the table, set REPLICA IDENTITY using ALTER TABLE.
+-- ok - insert and do nothing are not restricted
+MERGE INTO testpub_merge_no_ri USING testpub_merge_pk s ON s.a >= 1
+ WHEN MATCHED THEN DO NOTHING
+ WHEN NOT MATCHED THEN INSERT (a, b) VALUES (0, 0);
+-- ok - REPLICA IDENTITY is DEFAULT and table has a PK
+MERGE INTO testpub_merge_pk USING testpub_merge_no_ri s ON s.a >= 1
+ WHEN MATCHED AND s.a > 0 THEN UPDATE SET b = s.b
+ WHEN MATCHED THEN DELETE;
+DROP PUBLICATION pub1;
+DROP TABLE testpub_merge_no_ri;
+DROP TABLE testpub_merge_pk;
 RESET SESSION AUTHORIZATION;
 DROP ROLE regress_publication_user, regress_publication_user2;
 DROP ROLE regress_publication_user_dummy;

src/test/regress/sql/publication.sql

@@ -1250,6 +1250,37 @@ DROP PUBLICATION pub1;
 DROP TABLE testpub_insert_onconfl_no_ri;
 DROP TABLE testpub_insert_onconfl_parted;
 
+-- Test that the MERGE command correctly checks REPLICA IDENTITY when the
+-- target table is published.
+CREATE TABLE testpub_merge_no_ri (a int, b int);
+CREATE TABLE testpub_merge_pk (a int primary key, b int);
+
+SET client_min_messages = 'ERROR';
+CREATE PUBLICATION pub1 FOR ALL TABLES;
+RESET client_min_messages;
+
+-- fail - missing REPLICA IDENTITY
+MERGE INTO testpub_merge_no_ri USING testpub_merge_pk s ON s.a >= 1
+ WHEN MATCHED THEN UPDATE SET b = s.b;
+
+-- fail - missing REPLICA IDENTITY
+MERGE INTO testpub_merge_no_ri USING testpub_merge_pk s ON s.a >= 1
+ WHEN MATCHED THEN DELETE;
+
+-- ok - insert and do nothing are not restricted
+MERGE INTO testpub_merge_no_ri USING testpub_merge_pk s ON s.a >= 1
+ WHEN MATCHED THEN DO NOTHING
+ WHEN NOT MATCHED THEN INSERT (a, b) VALUES (0, 0);
+
+-- ok - REPLICA IDENTITY is DEFAULT and table has a PK
+MERGE INTO testpub_merge_pk USING testpub_merge_no_ri s ON s.a >= 1
+ WHEN MATCHED AND s.a > 0 THEN UPDATE SET b = s.b
+ WHEN MATCHED THEN DELETE;
+
+DROP PUBLICATION pub1;
+DROP TABLE testpub_merge_no_ri;
+DROP TABLE testpub_merge_pk;
+
 RESET SESSION AUTHORIZATION;
 DROP ROLE regress_publication_user, regress_publication_user2;
 DROP ROLE regress_publication_user_dummy;